A compact SWB MIMO antenna with 45° clock-wise square patch inclusions for polarization diversity applications

In this paper, a compact super wideband annular ring antenna using 45° clock-wise square patch inclusions for super high frequency and polarization diversity applications is proposed. The inclusions consist of a combination of squares and circles into one another in the inner area of a main annular ring radiator. The antenna uses a partial ground plane having a stair-type defected ground structure, is designed on an FR-4 substrate, and has a total size of 25 × 26 × 1.6 mm3 (0.17λ × 0.18λ). The design was fabricated and experimental results fairly agreed with simulations and resulted in an antenna with an operating frequency from 2.07 to 30 GHz; that is, a large fractional bandwidth of 174.2 with a bandwidth (BW) ratio of 14.5:1 and a high BW dimension ratio, BW per unit electrical length of 5693, and a measured peak gain of 8 dBi with an average gain of 5 dBi for the overall operating frequency. For the polarization diversity, a 4 × 4 multiple input-multiple output configuration is additionally presented, offering an effective isolation of ≥ 22.5 dB between ports and corroborated by measurements.